An (E)-7-[2-cyclopropyl-4-(4-fluorophenyl)-quinolin-3-yl]-3,5-dihydroxyhept-6-enoate is an intermediate which is useful as an intermediate for the synthesis of a HMG-CoA reductase inhibitor, and as its production method, the following method employing sodium borohydride (NaBH4) is disclosed in JP-A-1-279866, U.S. Pat. No. 5,856,336 or EP0304063B1:

Further, it has heretofore been known that at the time of producing a 1,3-diol by reducing a β-hydroxyketone by sodium borohydride, a boron compound is permitted to be present, as in the present invention, whereby a selective reduction reaction will proceed, and 1) JP-A-61-40243 or EP0164049A2 discloses a reaction in the presence of a triethylborane, 2) Chemistry Letters, 1980, 1415, discloses a reaction in the presence of a tributylborane, and 3) Chemistry Letters, 1987, 1923, discloses a reaction in the presence of diethylmethoxyborane.
Further, at that time, for the treatment of the boron compound after completion of the reduction reaction, in 1) and 2), the reaction solution with the tetrahydrofuran reaction solvent is per se poured into a 30% aqueous solution of hydrogen peroxide, and then, a solvent which separates from water, is added to carry out an extraction operation to obtain a product, and in 3), after the completion of the reaction, methanol is added, and an azeotropic operation with methanol is carried out, followed by a usual extraction operation to obtain a product.
As in the foregoing, in the reduction reaction of a β-hydroxyketone in the presence of a boron compound, it is necessary to carry out treatment of the boron compound after completion of the reduction reaction in order to efficiently obtain the product.
By the method for treating the boron compound after completion of the reaction as reported in the above 1), 2) and 3), there is no particularly serious problem in the production in a small amount at a laboratory experimental level, but in scaling up, the methods of 1) and 2) have an environmental waste liquid treatment problem due to the use of a large amount of an aqueous solution of hydrogen peroxide, and by the method of 3), unless a large amount of methanol is used, treatment of the boron compound can not completely be carried out, and there is a difficulty from the viewpoint of the production efficiency. Thus, either method can hardly be regarded as an industrially advantageous production method.
Further, with respect to the compound of the present invention, it has also been found that in order to isolate the desired substance from the product obtained after completion of the reduction reaction, it is necessary to carry out the treatment of the boron compound after completion of the reduction reaction, and otherwise, the desires substance can not easily be isolated.
Accordingly, it is an object of the present invention to provide a method for simply and industrially advantageously preparing an (E)-7-[2-cyclopropyl-4-(4-fluorophenyl) -quinolin-3-yl]-3,5-dihydroxyhept-6-enoate.